Hi,
In the enum class: TSEncoding, there's DIFF encoding, so when user want to choose a type of encoding algorithm(or input the wrong encoding type name), DIFF encoding is in the output hint and is one of IoTDB's recommending encoding type. But in IoTDB, DIFF encoding has not been added before,which I think may cause some problems. I think it's necessary to finish it. DIFF encoding algorithm is added now, PR's here[1] Both DIFF and TS_2DIFF encoding is based on delta encoding algorithm, so I finish DIFF using the similar interfaces and structure like TS_2DIFF to make it easier to understand. According to my understanding, TS_2DIFF is similar to the Delta of Delta Encoding algorithm, while DIFF is based on the delta Encoding algorithm, so TS_2DIFF performs better than DIFF. But DIFF's algorithm is relatively simple, and it's one of the first algorithms for people who are new to data coding(like me) are exposed to. Here's the performance report: [2]. This is my first time to submit the code to the community, and there may be some problems. So really look forward to your review and advise:) I will continue to learn and try to contribute better code to the community! Thanks, Ruizheng Wu [1] https://github.com/apache/iotdb/pull/1890 [2] https://cwiki.apache.org/confluence/display/IOTDB/DIFF+encoding%27s+perfomance
